Carburetor



United States Patent Inventor James H. Currie Rochester, Michigan Appl. No. 765,398 Filed Oct. 7, 1968 Patented Dec. 1, 1970 Assignee General Motors Corporation Detroit, Michigan a corporation of Delaware CARBURETOR 1 Claim, 7 Drawing Figs.

U.S. Cl,

Int. Cl.

Field of Search References Cited UNITED STATES PATENTS 1,736,239 11/1929 Wilson Primary Examiner-Tim R. Miles Attorneys-J. L. Carpenter, W. F. Wagner and C. K. Veenstra ABSTRACT: The disclosed carburetor has three barrels-two conventional barrels designed to deliver air-fuel mixtures over the broad range of open-throttle operating conditions and a small third barrel designed to deliver the air-fuel mixture during closed-throttle idling conditions. The small third barrel has a venturi to provide an idle fuel-metering signal and a fixed throttling restriction below the venturi to control the rate of flow. The idle fuel passages which deliver fuel into the third barrel venturi also have transfer ports opening into the main barrels above the throttles to provide a smooth transition from idling operation to open throttle operation.

Patented Dec. 1, 1970 Shed INVIiNI'uR Jbmes H.Curr1'e ATTORNEY Patented Dec. 1, 1970 I 3,544,083

Shut 3 0:2

James 11. Carrie- ATTORNEY CARBUIRETOR BACKGROUND OF THE INVENTION A number ofrecent proposals for improving carburetor operation have recommended multiple stage carburetion in which the primary carburetor'venturis are quite small so that accurate proportioning of the air-fuel mixture may be achieved in the low airflow ranges. In some of these proposals, the primary carburetor has been designed to control the airfuel mixture over a substantial portion of the part-throttle operating range; other proposals, on the other hand, have suggested that the primary carburetor should not be required to control the air-fuel mixture over much more than the narrow range of idling engine operation.

SUMMARY OF THE INVENTION This invention provides an internal combustion engine carburetor, suitable for automotive applications, in which one or more main barrels are designed to control the air-fuel mixture over substantially all of the open-throttle operating range in a generally conventional manner and in which a small additional barrel controls the air-fuel mixture during idling operation of the engine. A venturi disposed in this small barrel provides the fuel-metering signal which assures that idle fuel flow will be properly proportioned in accordance with idle airflow. An adjusting valve disposed below the venturi controls airflow through the additional barrel to provide an accurate setting for the idle airflow. To permit a smooth transition of fuel-metering control from the small barrel to the main barrel, the idle fuel passage has a transfer port arrangement opening into the main barrel adjacent the upper edge of the main barrel throttle.

The details as well as other objects and advantages of this invention are shown in the drawings and discussed in the description of a preferred embodiment.

SUMMARY OF THE DRAWINGS FIG. 1 is a side elevational view of a three barrel carburetor incorporating two main barrels and a small additional barrel;

FIG. 2 is a top plan view of the fuel bowl section of the carburetor, taken generally along line 2-2 of FIG. 1 with the air horn section removed, to show the disposition of the inlet to the small barrel relative to the venturi cluster and the main barrels;

FIG. 3 is a sectional view of the carburetor taken along line 3-3 of FIG. 2 showing the small barrel;

FIG. 4 is a bottom plan view of the carburetor illustrating a recess which provides the opening from the small barrel into the two main barrels;

FIG. 5 is a top plan view of thethrottle body section of the carburetor, taken generally along line 5-5 of FIG. 1 with the air horn and fuel bowl sections removed, illustrating the fuel passages which extend to the small barrel;

FIG. 6 is a sectional view of the carburetor taken along line 6-6 of FIG. 2 illustrating the main fuel system and portions of s the idle fuel system; and

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the carburetor 10 includes a throttle body section 12, a fuel bowl section 14 mounted on throttle body 12, a venturi cluster 16 secured by screws 18 within fuel bowl section 14 (as shown in FIGS. 2 and 3), and an air horn section 20 mounted on top of fuel bowl section 14.

Carburetor 10 includes a common air inlet 22 which is controlled by a choke 23 in the conventional manner. A pair of main barrels or air passages 24, containing venturis 26, extends from air inlet 22 and is controlled by throttles 28 in the conventional manner.

As shown in FIG. 6, fuel is supplied to main air passages 24 from a fuel bowl 30 which contains fuel maintained at a substantially constant level by a float mechanism 32. Each main air passage 24 has a separate fuel-metering system, only one being shown and described since the systems are identical. For each' main air passage 24, fuel is metered from fuel bowl 30 through a main metering restriction 34 into a main well 36. A fuel delivery tube 38 depends from venturi cluster 16 into main well 36 and delivers fuel into an auxiliary air passage 40 which has a discharge point in a boost venturi 42 located within main air passage venturi 26.

The construction thus far described is conventional and has been set forth only to the extent necessary for an understanding of the present invention.

A small additional barrel or idle air passage 44 extends from an opening 46, disposed in common air inlet 22 between main air passages 24, to a recess 48 formed in the base of throttle body 12 as shown in FIGS. 3, 4, and 7. Recess 48 interconnects idle air passage 44 with main air passages 24 and discharges flow from idle air passage 44 into main air passages 24.

Again as shown in FIG. 6, main wells 36 also provide fuel for a pair of idle tubes 50 (only one being shown) which depend from venturi cluster 16. Each idle tube 50 discharges through its own idle fuel passage 52, each of which extends down through fuel bowl section 14 into throttle body 12. As shown in FIGS. 5 and 7, horizontal passages 54 are formed in throttle body 12 and extend from passages 52 to idle fuel discharge points 56 formed in a venturi 58 disposed in idle air passage 44. A pair of metering restrictions 60 are provided in passages 54 to control the rate of idle fuel flow into idle air passage 44.

As shown in FIGS. 5, 6, and 7,each idle fuel passage 52 has one or more transfer ports 62 and 64 opening into a main air passage 24 adjacent the upstream edge 66 of throttle 28. Fuel flow to venturi 58 through passages 52 is directed near transfer ports 62 and 64 to eliminate any lag in fuel discharge through the transfer ports.

An adjusting screw 68 extends into idle air passage 44 below venturi 58 to provide a fixed throttling restriction for control of the rate of flow through idle air passage 44. As shown in FIGS. 2 and 5, main throttle shaft 70 has a lever arm 72 carrying another adjusting screw 74which bears against a projection 76 extending upwardly from throttle body 12. To adjust the engine idling speed, closing movement of throttles 28 is limited to a position lightly cracked from the tightly closed position by turning in screw 74 against projection76, thus allowing a slight airflow directly through main air passages 24 about throttles 28. Since throttles 28 are only lightly cracked, however, the bulk of idle airflow will be drawn through idle air passage 44 past venturi 58 and discharged through recess 48 into main air passages 24 below throttles 28. Screw 68 is then adjusted to control the rate of airflow through idle air passage 44 and thus accurately control the idle speed of the engine.

With the throttle 28 in the lightly cracked but essentially closed position as shown and described, venturi 58 creates a vacuum metering signal which varies in accordance with the rate of airflow through idle air passage 44. The metering signal draws fuel from fuel bowl 30 through the main jets 34, main wells 36, idle tubes 50, idle fuel passages 52, passages 54, and idle fuel metering restrictions 60 into idle air passage 44. As throttles 28 are opened to increase the airflow and thus increase engine speed, the upstream edges 66 traverse transfer ports 62. The vacuum below throttles 28 then draws fuel from idle fuel passages 52 through ports 62 directly into main barrels 24. As throttles 28 are opened further, transfer ports 64 are exposed below the throttle blades and fuel flow from idle fuel passages 52 is increased. With the opening of throttles 23, of course, air flow through main venturis 26 and boost venturis 42 starts fuel flow from fuel bowl 30 through main mete ring restriction 34 and fuel tube 38, but fuel discharge through transfer ports 62 and 64 provides a smooth transition as control over the air-fuel mixture is transferred from idle air passage 44 to main air passages 24.

Although idle air passage 44 could have its inlet 46 disposed at a location within main air passages 24 above throttles 28, the disposition of inlet 46 within common air inlet 22 above venturis 26 is preferred; this arrangement minimizes airflow through venturis 26 and 42 during idling operation and thus eliminates the possibility that idle airflow through venturis 26 and 42 will cause fuel to drip from the main fuel tubes 38. Of course, idle air inlet 46 could be located entirely apart from common air inlet 22 and main air passages 24 if the advantage of a compact structure is not essential.

Although not specifically shown in the drawings, it is considered preferable to provide air bleeds into the idle fuel metering and delivery systems to form an emulsion of air and fuel in idle fuel passages 52 as is conventional practice.

It will be appreciated that the foremost advantage of the construction set forth above lies in the fact that the idle fuel flow ismetered and delivered into the idle airflow at a point where the idle airflow velocity is very high. This arrangement promotes efficient mixing of the idle fuel and air, permitting somewhat leaner operationwith the concomitant potential for increased fuel economy and reduced emission of objectionable exhaust gas constituents. In addition, the efficient mixing of the fuel and air enhances engine starting and improves distribution of the mixture through the manifold.

This construction also simplified adjustment of the engineidling conditions. Adjusting screws for idle fuel flow are not necessary since idle fuel flow is metered by the venturi vacuum signal past fixed restrictions 60 installed during manufacture of the carburetor. Adjustments for balancing idle fuel flow through the separate idle fuel passages 52 are not necessary since idle fuel is supplied to both main air passages 24 from a single idle passage 44. While two adjusting screws 68 and 74 are provided for control ofidle airflow in order that adjusting screw 68 may give very precise control, the additional adjustment provided by screw 74 may be unnecessary in many cases.

lclaim:

1. An internal combustion engine carburetor comprising a common air inlet, a pair of main air passages extending from said air inlet, a pair of throttle valves respectively disposed in said air passages and simultaneouslyrotatablc between closed and open positions for controlling flow therethrough, a fuel bowl, a pair of main fuel passages respectively extending from said fuel bowl to main fuel discharge points in said air passages for delivering fuel from said bowl to said passages under openthrottle operating conditions, a pair of idle fuel passages respectively extending from said fuel bowl to said air passages and having ports opening into said passages only at locations which are upstream of the upstream edges of said throttle valves when said throttle valves are in closed position and which are traversed by the upstream edges of said throttle valves as said throttle valves are rotated from closed to open position whereby said ports deliver fuel during the transition from closed throttle operating conditions to open-throttle operating conditions, an idle air passage disposed between said main air passages and extending from said common air inlet and opening into said main air passages at locations downstream of said throttle valves, each of said idle fuel passages further extending to an idle fuel discharge point in said idle air passage for delivering fuel under closed-throttle operating conditions, a venturi disposed in said idle air passage at said idle fuel discharge point for creating a vacuum signal which will draw fuel from said fuel bowl through said idle fuel passages into said idle air passages at a rate varying in accordance with the rate of airflow through said idle air passage, and a control valve disposed in said idle air passage downstream of said venturi for controlling flow therethrough. 

